1. Field of the Invention
The present invention relates to a portable information device such as a portable telephone terminal, portable information processing terminal or the like, and in particular to a portable information device having an action detecting function.
2. Description of the Related Art
To increase portability, portable information devices including portable telephone terminals are becoming smaller in size. However, for such miniaturization, display visibility and input operability are traded off. Recently, several techniques of increasing the input operability without degrading portability have been proposed.
Japanese Patent Application Unexamined Publication No. 2003-5879 discloses a portable information terminal having a rotating operation detector. The rotating operation detector detects a tilt of the terminal body rotating around one of predetermined axial directions (X, Y and Z axes) and, determines whether the terminal body tilts in the direction of a scroll arrow, typically one of upward, downward, rightward and leftward arrows, displayed on screen. When the tilt matches the scroll arrow, scrolling is started on the display.
Japanese Patent Application Unexamined Publication No. 2003-114752 discloses a portable information terminal device having a tilt detector and a controller controlling display of two rings of icons depending on a detected tilt direction. More specifically, the icons in the one ring are sequentially foremost displayed depending on the rightward/leftward direction of tilt and, after one icon has been selected from the one ring, the icons in the other ring are sequentially foremost displayed depending on the upward/downward direction of tilt.
Japanese Patent Application Unexamined Publication No. 2002-149616 discloses an information retrieval terminal having an acceleration sensor, which is used to detect a gesture of a user shaking or tilting the terminal body. The movement of displayed icons is controlled depending on a tilt angle of the upward, downward, rightward or leftward direction. When the terminal body is shaken, the retrieval is terminated.
However, the above-mentioned prior arts can detect only two dimensional movements such as rotation operations in the upward/downward direction or rightward/leftward direction of tilt. Further, the portable terminal itself cannot determine an absolute bearing with respect to the geomagnetic field. The information retrieval terminal (Publication No. 2002-149616) may determine its absolute bearing by placing the terminal body on the cradle.
Japanese Patent Application Unexamined Publication No. 2001-033253 discloses an attitude and angle detector using gyroscopes, geomagnetic field sensors and an acceleration sensor to detect an action of a device body. However, such a structure is not suitable for a portable device which is becoming smaller in size. In addition, gyroscopes are sensitive to physical shock. Therefore, when dropped, the attitude and angle detection is easily damaged because of breakage of gyroscopes.